From fresh to saline: a comparison of zooplankton and plant communities developing under a gradient of salinity with communities developing under constant salinity levels

Abstract

In Australia, many freshwater wetlands are becoming saline. Knowing which elements of a biotic community will persist as wetlands turn saline is relevant to their future management. We simulated gradual and sudden increases in salinity in outdoor mesocosms to test the hypotheses that: (1) aquatic plant and zooplankton communities exposed to a gradient of increasing salinity over time would initially resemble freshwater communities, but as the salinity increased they would resemble communities found in more saline systems; and (2) that a gradual change in salinity over 6 months influences zooplankton and plant communities in the same way as a sudden salinity change. Below 1000 mg L–1, as salinity increased gradually, communities rich in species and numbers of individuals resembled freshwater communities. However, as the salinity exceeded 1000 mg L–1, taxa were progressively lost and communities became less diverse. When salinities exceeded 3000 mg L–1 the diversity decreased rapidly and few taxa remained at 5000 mg L–1. Both sudden and gradual increases in salinity induced similar decreases in diversity. We predict that as natural wetlands become more saline, few freshwater biota will survive once the salinity exceeds 5000 mg L–1. In the long term, such salinised wetlands would need to be recolonised by salt-tolerant taxa for a functional wetland to persist.

Genetic variability in the tolerance of natural populations ofSimocephalus vetulus(Müller, 1776) to lethal levels of sodium chloride

“…In coastal lakes that face regular (e.g., tidal) or sporadic salinity increases, freshwater organisms must cope with potentially lethal levels of salinity for short-term periods (hours to days). Particularly for large cladocerans (such as Daphnia and Simocephalus), their ability to survive (or not) these salinity pulses may modulate zooplanktonic taxa succession (Jeppesen et al, 1994(Jeppesen et al, , 2007Schallenberg et al, 2003;Nielsen et al, 2008) and a lake regime shift (see Jeppesen et al, 2007).…”

“…Saline intrusion in freshwaters has received considerable attention (e.g., Schallenberg et al, 2003;Sarma et al, 2006;Gonc¸alves et al, 2007;Nielsen et al, 2008), justified by the predictions of sea level rise and observation of coastal erosion, which threaten coastal lakes (IPCC, 2008). In coastal lakes that face regular (e.g., tidal) or sporadic salinity increases, freshwater organisms must cope with potentially lethal levels of salinity for short-term periods (hours to days).…”

Long‐term effects of salinity and disturbance regime on active and dormant crustacean communities

“…Wetlands in general and temporary wetlands in particular are among the ecosystems most threatened by climate change, since they are very sensitive to changes in quantity and quality of their water supply (Pyke 2005;Erwin 2009). Climate change can result in changes in precipitation patterns, runoff, temperature, and sea level; parameters that affect wetlands in two fundamental ways: quantitatively, the number of functioning wetlands may decline, and qualitatively, the remaining wetlands may undergo shifts in their hydrological cycles and water quality (including salinity) (IPCC 2007;Erwin 2009;Nielsen and Brock 2009). In addition, the growing demands for irrigation and drinking water imply increased anthropogenic stress that may alter the water balance and water quality of wetlands (Angeler 2007;IPCC 2007;Nielsen and Brock 2009).…”

“…Climate change can result in changes in precipitation patterns, runoff, temperature, and sea level; parameters that affect wetlands in two fundamental ways: quantitatively, the number of functioning wetlands may decline, and qualitatively, the remaining wetlands may undergo shifts in their hydrological cycles and water quality (including salinity) (IPCC 2007;Erwin 2009;Nielsen and Brock 2009). In addition, the growing demands for irrigation and drinking water imply increased anthropogenic stress that may alter the water balance and water quality of wetlands (Angeler 2007;IPCC 2007;Nielsen and Brock 2009). Any hydrological modification or change in salinity is predicted to strongly affect species composition and ecosystem functioning of wetlands and result in shifting species distributions and extinctions, especially for species that are already at the edge of their ecological range (Poff et al 2002;Nielsen and Brock 2009).…”

“…In addition, the growing demands for irrigation and drinking water imply increased anthropogenic stress that may alter the water balance and water quality of wetlands (Angeler 2007;IPCC 2007;Nielsen and Brock 2009). Any hydrological modification or change in salinity is predicted to strongly affect species composition and ecosystem functioning of wetlands and result in shifting species distributions and extinctions, especially for species that are already at the edge of their ecological range (Poff et al 2002;Nielsen and Brock 2009). This is particularly true across more fragmented landscapes because of the continuous decline in wetland number and anthropogenic alteration of the environment, limiting the ability of species to reach suitable habitats.…”